Mustard gas, or sulfur mustard, is a notorious chemical warfare agent historically used in conflicts such as World War I. Although commonly referred to as a “gas,” the agent is technically an oily liquid at room temperature. This physical property is often misunderstood, leading to mischaracterizations of its potential for combustion and other dangers.
The Fire Hazard of Mustard Gas
Mustard gas is not considered highly flammable like gasoline or other volatile organic compounds. It is classified as combustible, meaning it can burn, but it does not ignite easily and is not explosive. The substance is an oily, yellowish-brown liquid with a relatively high flash point, typically around 104°C to 105°C (219°F to 221°F). This high flash point indicates that significant external heat is required to produce enough vapor to sustain a flame.
When combustion occurs, it is often slow, and the primary danger shifts to the toxic byproducts created. Burning mustard gas releases highly toxic fumes, including sulfur oxides and hydrogen chloride, posing an immediate and severe chemical inhalation hazard.
Primary Danger: Chemical Vesicant
The overwhelming danger of mustard gas lies in its function as a powerful vesicant, or blister agent, and its mechanism as a potent alkylating agent. It causes severe chemical burns and blistering on contact with tissue. As an alkylating agent, it rapidly reacts with and damages DNA, RNA, and proteins within cells, leading to delayed but catastrophic cellular injury. This ability to chemically alter genetic material also makes it a known human carcinogen, particularly linked to respiratory tract cancers years after exposure.
Exposure to the liquid or vapor leads to a delayed onset of symptoms, which can lull victims into a false sense of security. Skin exposure first causes erythema, or redness, often appearing within four to eight hours, followed by the formation of large, painful blisters. Areas with thin or moist skin, such as the eyes and genital region, are especially susceptible to rapid damage. Ocular exposure results in intense irritation, lacrimation, and swelling of the eyelids, which can progress to severe corneal damage and potential blindness.
Inhalation of mustard gas vapor causes internal chemical burns, leading to severe damage to the respiratory tract’s mucous membranes. This can cause bleeding and blistering within the airways, potentially resulting in pulmonary edema, a life-threatening accumulation of fluid in the lungs.
Response to Heat and Neutralization
Even when it does not ignite, subjecting mustard gas to heat significantly increases its toxicity by enhancing its volatility. As temperatures rise, the liquid evaporates faster, increasing the concentration of toxic vapor in the surrounding air. When heated to decomposition, typically between 149°C and 177°C (300°F and 350°F), the substance breaks down into highly toxic fumes.
Neutralization and decontamination procedures are designed to render the agent inert through chemical reaction. For practical decontamination of surfaces and equipment, strong oxidizing agents, such as bleach solutions, are commonly used to chemically destroy the mustard agent.
Sulfur mustard can also react with water in a process called hydrolysis, slowly forming less toxic products like thiodiglycol. Specialized large-scale destruction methods may involve thermal processes or reactions with metallic powders to ensure complete detoxification.